In known air classifier systems there is provided a rotary drum classifier which is positioned at a fixed angle of inclination so that a stream of air may be made to flow through the drum at a fixed velocity to separate materials deposited within the drum. Such materials are usually transported to the drum by a conveyor which has one end extended into the drum so that the materials may be deposited therein at a point near the longitudinal center of the drum.
It is also known that the angle of inclination of the drum may be changed, if desired. This will effectively alter the velocity of the air flowing through the drum and so change the ratio of lights-to-heavies in the materials being separated. In some known systems the higher end of the drum is positioned within an opening in a separate fixed processing chamber such as a plenum, for example. In such a case the angle of inclination of the drum must be changed by raising or dropping the lower end of the drum, even though a conveyor or other feed device is mounted within this end. However, it will be apparent that with a conveyor penetrating a substantial distance into the drum, this will create difficulties in the achievement of such angle change, especially if the conveyor is relatively larger or the drum diameter is relatively short.
If the drum receives its supply of materials from a supply hopper which is mounted on the same adjustable platform as the drum, difficulties are created when the hopper is moved, since the hopper usually is loaded by a separate conveyor. Thus, movement of the hopper, when the platform is adjusted, may move the hopper out of proper spacial relationship with the conveyor. This problem is particularly acute when the hopper supports one end of a feed screw by which the drum is loaded and thus must be moved with the platform to retain proper relationship with the drum, particularly in cases where the hopper is adjustable independently with respect to the drum.